Transmission regulating circuits



Patented Aug. 2d,

Masera MEfS-mfrasj' PATENT orales..

' .GEORGE caisson, or HACKENSACK, Niiw .mizsnmnsseiron 'ro AMERICAN TELET HOIBTE TELEGRAITH COMPANY, A CORPORATION OF NEWNYORK.

TRANSMISSION REGULATING CIRCUITS.

Appucatin aiea'irarh c, 1921. `serial-ita. 450,352.

To all whomy t may concern.'

Be it known that l,"GEoRGE vCRIssoN, re-4 siding at Hackensack, in the county of Bergen and State of-New-Jersey, have invented certain improvements in Transmission Regulating Circuits, of which the following is.

'a specification.

This invention lrelates to signaling circuits and morel particularly to arrangements for .controlling the. transmission equival'ent of such circuits.

It has been found that-:the transmission.

equivalent'of'signaling circuits such, for example, as telephone circuits,v .varies from I vtime to time, due 'to `anumber-of causes, theV principal of which is a change in resistance producedby.temperature,variations. c As `it -jis common practice to-'carry the Wires ofy a.

number .of 'telephone circuits along the 'same ngzopole line or throughv the same hcable, it is apparent that all of the lines thustreated lwill be subject vto substantially the same y changein-temperature conditions. It/has,

vva cable, l'for example, and then varying inY therefore, beenA 'proposed to overcome the diliiculties due to these variations by observ-v ingl the changes producedin one circuito-f `accordance with such changes Isimilarl transmission elements of all ofthe circuits which are affected in like manner.

l the transmissionelements in proper propor f tion to the change in' lresistance of the pilotl circuit, tlie"transmission'equivalent of all of the circuits may be dmaintained constant' so` far as resistance changes with tempera-'- ture are concerned. This method may, `ot y course. be carried out by measuring the `current in the pilot circuit in: any Well known *',nianuer` and then making the 'changes' lin 'the transmission elenients'ofthe other circuits manually, or it.may be carried outby providing apparatus Whichiautojmatically responds to changesin the current flowing j in the pilot. circuit to perform the' necessary adjustments in the other circuits, by means ofsuitable 'switching arrangements. Appa-l ratustorcarrying out the method automaticallyis disclosed in the U. S. application of A. B.. Clark, Serial No.v 253,486, filed Septomber 10, 1918,*patented Dec. 12, 1922,A No'.

In the practice ofthe method above outsides ofthe pilot circuit in parallel.

-By varying is frequently rundesirable to arrange this apparatus atthe terminal of the pilot circuit,

.to temperatureV .variations in exactly the samewaywhen serially included in the pilot, i `circuit at an intermediate point, a' difiiculty has ,been encountered in connection with .such an arrangementot the apparatus, due toI disturbingcurrents inducedfrom neigh-- boring circuits and/Hearing4 over the two 'One of the principal objects of this linven- :tionis to' provide ,i arrangements for over-4 :coming this difiiculty, although other objects of the invention will be clear from the following description of the invention,l

. and it should preferably be located at some v intermediate point. XVhile `the vmeasuring instrument or currentresponsive device Will .function to. record changes in resistance due when re'ad in connection'fwith'the accom--` panying drawing, schematic diagram of a pilot Wire with the measuringvinstrument or current responsive .device serially included therein at an interin Which'Fieure 1 is a' mediate point'; Fig, 2 illustrates the appara- ,tus bridgedA across the pilot wire 'at an ini termediate point4 in accordanceY With-the present invention ;f Figs. 3 and'i4- V'illustratel the same arrangement provided lwith, means'l for compensating for the, dilierence in-v the ,two loops of the pilot'circuit oneach. side of the current responsive device; while Figs.-` 5 v and 6 are curvesill'stij'ating the chal'iu'ter#` isti'cs of the apparatus of`the presentinv.en-f

tion.

Referring to theidravvings, Fig.- 'il'sliofws av .pilot Wire 1, forming partof one armof a llheatstonefbridge, of which resistances',` 3; Thel bridge is supplied. with, a" battery 5 connected across'.V Vthe'two opposite. terminals tliereoffand a' and 4 lforni the( otherjarms.

measuring instrument 6 is connected' across thel other two points of thebridge. This'arrangement is schematiciand is 'illustrativef of meansvwhich'would be employed for ob-.

mission equivalent.

4 ductor carrying serving the changes in resistance in the ,pilot Wire circuit where the adjustment of the transmission elements of the telephone circuits is to be performed manually. Obviously the device 6 may be instead of a measuring instrument a current respon. ive device for automaticallyi conltrolling ille transmission elements of the Various telephone circuits as disclosed in the Clark application previously referred to. It will be noted that in Fig. 1, the measuring instrument and associated apparatus isserially includedin the pilot circuit 1 atan intermediate point 5. This arrangement has been found to be satisfactory as long as the pilot Wire conductors are not exposed to induction, but if one of' the loops as, for ex# ample, the West loop, is paralleled by a con- Morse or other currents, a charge Will be induced upon the tWo Wires of the West lo'op Which causes momentarycurrents to flow over the two Wires of the West vloop in parallel. The flow of these currents in the Wire which is out directly through from West to east, does no harm, but the current in the other Wire passes through the regulatingapparatus and causes the current measuring instrument 6 to give a false reading, or in the case ot the automatic apparatus of the Clark application previously referred to, causes the galvanometer relay' correspondingr to the device 6 to chatter and produce false operation of the automaticv gain controlling mechanism. in order to overcome this diliculty it-is proposed in accordance with the present invention to connect the east and West loops in parallel with the terminals of the meatstone bridge arrangement bridged across the loops as illustrated in Fig.. 2. This will permit the current responsive device 6 to measure the joint resistance of the `two loops so `that the trouble from induction can he eliminated. The two Wires extending to the east-are ac- :panacea curately balanced with respect to their surroundings, as are the me Wires extending to the West. Consequently, when one pair is exposed to induction from a neighboring conductor, equal currents *flow over the two Wires into the other pair and no difference in i potential is produced between the points connected'with the bridge. r`lhe balance of the bridge is thereae undisturbed, provided it is insulated from the earth.

ln the series arraneement of Fi l the joint resistance of the two pilot Wire loops 1s the sum of the resistances ot the separate loops, that is Bezigil-Rz joint resistance llp is given by the formula n :aan

Assume that one of the loops. tor en ample, R1, changes its resistance by an amount r, and that the resulting change in the joint resistance is rp, then the new condition is given by the formula Substituting the value of Rp from (2) and transposing RpJrrp:

From this equation it is readily seen that it the initial value R, ot the varied resistance is greater than R2 the change rp in the joint resistance Rp is small and R, is smaller than Re, 'rp is large, that is,l ifione loop has less resistance than the other, the loop of lower resistance has the greater effect upon the joint resistance. This is undesirable as the-.longer -portion ot' the transmission circuit associated With the pilot cirn cuit has the greater effect upon the translVhere it is impossible to locate the controlling apparatusv exactly at the middle ol the pilot wire so that the two loops will be equal, the influence of the shorter loop will be greater than the z (Escala D 21,4- B, +R2 ltl-l-RZ Simplifying: y

' 7'1' (e l il fl Rj i il l Re) (l 'Jr Rf longer loop, unless some means he provided 'to compensate for this effect. -ln accordance-With the present invention` it is. therefore, proposed to include in the shorter loop a constant compensating resistance suolx as the resistance 7 of Fig. 3.

the compensating Aresistance as being inserted at the distant end of thc shorter loop. Where it is desired to include vthe compensating resistance at the same point as the controlling apparatus, the resistance may be divided intoltivo equal parts, and one part put in series withA each conductor ot' the short loop, as illustrated in Fig. l. A ysingle resistance cannot be used in the latter ease as it lwould unbalance the system with rewhicli illusirates spect to disturbing induced currents, and therefore vdefeat the object of the parallel arrangement.

Vlhen'the loops are' givenequalresistance by providinga compensating resistance forV the shorter loop, thef'ell'ect of a given change in temperature upon the resistanceJof-either loop'is proportional totheA length .ofthe pilot Wirein that loop,` and is therefore' propoi-tional to. the change in transmission equivalen-t produced lin the corresponding" portion of the transmission circuit, assuming-.ot course, that the pilotfwire Iis ot uniform diameter;A throughout. its. vlength'. However, with theparallel arrangement, changes in. joint resistance are not exactly proportionalto the chances in -the resistances of the individual loops as in the series arrangement although for the range otrariations encountered y in pilot Wires in practice, theapp'roximation is 'sufficiently-close so vthat no dilliculty is encountered from these sources.

'The effect of this-*factorwvillbe clear from a considerationn the curves illustrated in F ig. 5. vIn theSe'curVes the behavior of theV of 'the otherloop increases The curve B 'is :loops is compared and 'series-'and parallel arranqeuientsol the two two loops are initially-of equalresistance, and that one or both varies fromv the initial y 'reentage 4Curves A, B C and yD are plottedwith the values ot' the `resistance change inepercent'ageas the abs,cissae vand the ratio lof `joint resistance to normal joint resistance' in percentage'as ordina-tes'. vThe 'curve A represents .the variation in the ratio' of v com loined resistance t0' the n'ormal .joint resistance fortheseriesar-- rangement ot Figi 1,. )vliet-e the 'resistanceof one loop remains normal and the resistance a plot under the vsame Aconditionsofthe lcom-A bined resistance of' a' parallel arrangement Such as.` that illustrated in Fig. 2. The curve ,C isa plotfor'theseries casefwherethe 'refv sistance of one loop remains 'normal'and the resistance ol the other loop-decreases. Curve D is agsimilar, .curve for .the parallelarvrangement. Curves A C- show that lwhen one4 loop varies, therpercentage changef.

of. thejoin-t series'res'istance i'sonehalf A.

A. comparison-otthse curves With'curves B and D shows that the per cent increase of thev joint parallel 'resistancezis slightly .less .r and the' per cent' ldecrease Aslightly greater f than the 'per cent Qchauge'in the joint series resistance. Curve near the" horizontal axis is plotted W'ithvthe differences 'between the seriesand parallelcombined rsistances.

as ordinatesfand shows the dilference between 'the series. and parallel arrangements l.1s assumed .that thevv americano' o ro-(14m) in per centotthe normal value. As'willbe seen, this ditlerence is relatively small and need not be considered.

If one loop should. increase and one decrease in resistance by equal percentage there would be no change in the joint series resistance, this being indicated by the curve Gwhich coincides with the horizontal axis. The joint parallel resistance would decrease,

however, .as indicatedfby the 'curve ll.

lhile this curve showsia considerable deviation from the ideal conditionrepresented would probably neverloccur vin practice, as theline sections to which the invention applies are usually limited to between 200 and 30() miles. Consequently, Athe tivo loops will not-bel subjected simultaneously to opposite extremes of temperature.l

Another factor to be Aconsidered vis the by the curve G. this vparticularj'situation effect Vof the compensating`iesistancc such as the resistance 7.on the accuracy `0l: the

. arrangemenhritbeing noted that while the resistance of the line Willv vary with uniform temperature changes, the compensating resistance will not vary, and conse.

que-ntly, Where'both loops. are subjectedl to ofboth varies, :1n error is introduced. This .-error can be found as follows: Let' Rzinitial resistance A of each loop.

` zfzfractional changein resistance ot' the loop wires due to change in temperature. f

the .compensated loopwhich is in the loop conductors.

l'-71:fractionfin the con'ipensatingres istance.

rplzchange in joint resistance ot' -t compensatedv system. l

Then the changed resistanceot thc uncompensatedloop is R(lllt) vand in the coni- -pensated loop Y i Home R 1+fr= 1+ncu The jointvaried resistance is stood 4from the following theorct ical con-I 1. An :the fraction of theV resistance of 4isaluna "i i I I l l u l li li no compensiting resistance n l and Multlplymg each Side by and remembep l RD+1H 1 +033 (6) The difference between the compensated and nouw upcusated systems from (5) and (6) is ing that Vit is l'ound that the difference in joint resistance between the ionipensated and nonconipensated systems is closely proportional to the `change in resistance of the pilotwire conductcu's and the compensati-d system acts in very nearly the same way as a noncompensated system of conductois having a somewhat smaller temperature coetlicient over the ranges likely to be encountered iu practice. For example, from the curve drawn for the case Where arf), the dil'erence bctweentlie joint resistance of a coinpensated system and that ol a noncompensated system is only about .T of 1%, when the variation in conductor resistance is as high as laf/2). Even in the case where azi), the dii'lerence between the resistance of the compensated system and that of the noneoiupensated system .is only 3.6% tor a variation in conductor.resistance ot lato/0. r-l`he error cause by a given amount of compensating `resistance can, therefore, be

rorrected by using slightly smaller steps in the adjustable transmission elements o't' the telephone circuits. Of course, when there no` compensating resistance and uniform temperature changes occur throughout the system, no ei'ror is produced by the parallel arrangement, for the whole system changes uni liormly.

lVhile the parallel pilot Wire arrangement does not give precisely the changes in resistance theoretically required to produce an exact equalization ol transmission for all possible temperature conditions, the degree of approximation obtained when correction is made by the insertion ot' compensating resistances iu the low resistance loop (Where required), is so close fo any probable teinperature condition that no serious dilliculty will be encountered iu its use, and it does have thc advantage ol preventing disturbances of the controlling` apparatus by induced charges llowing ironi one loop to the other. l

While in the foregoingr discussion an automatically operated lVheatstone bridge has been assumed as the device which responds to the pilot Wire variations, nevertheless the discussion lapplies equally Well to any equivaient arrangement. Furthermore, it will be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those ing the adjustments to be made in the signaling circuits to compensate for the change.

in transmission, said apparatus being bridged across the conductors of the pilot circuit at a point intermediate the ends'of said circuit and being balanced. with respect to the two sides of the pilot circuit.

2. ln a signaling system, a group of signaling conductors similarly subjected to conditions producing variations in. their transmission eliiciency, a pilot circuit subjected to the same conditions as the signaling conductors. and an 4apparatus for determining the adjustments to. be made in the signaling circuits to compensate -for the change in transmission, said apparatus being Ybridged across the conductors of the pilot circuit at a point intermediate the ends of said circuit so that the loop of the pilot circuit on one side oi the point off connection is longer than the loop on the other side, said apparatus alsobeing balanced with respect to the two sides Aof the pilot circuit 3. In a signaling system a group of sig- I naling conductors similarly subjected to conditions producing variations in their transmission eclency, a pilot circuit subjected to thesaiiiei conditions as the signaling conductors, an apparatus for determining the adjustment to be'inade in the signaling circuits to compensate for the change in transmission, said apparatus being bridged across tli/e conductors of the'pilot circuit at a point intermediate the ends of said. circuit/ so that the loop 0f the pilot circuit on one side of the point 0f connection is longer than the loop on the other side,l and iis means included inthe shorter loop t0 compensate for the difference in the length of the'ftwo loo s.' 'f' 4. In a signaling system, sgroup of sig- `naling' conductors similarlysubjeeted to conditions producing variations in their transmission eiiciency, a pilot circuit subjected to the same conditions vas theffsignalng oonductors, an 'apparatus forfvdeterinini fig the adjustments t0 be made in the signaling.,r circuits tov compensate for' the change in tra-nsimission; said 4apparatus being 'bridgedv eisv fmission eiiiciency, a pilot rcircuit subjected to the same conditions as the signaling conductors, :inapparatus OPdeterminingthe* adjustment-sto be made in the signaling-cir- -cuitysto compensate forthe-changein'transmission, said apparatus'f being bridged `across the conductors yof" the pilot circuitlat a poin't intermediate theendsl of said cir- "cuit so-tliatthe loopen one side of the pointl of connection' has a greater' resistance than that of thel loop' on 'the others'ide, and AmeansY included in the loop having the' smaller resistance to compensaite yfor the difj loops.'

ference between the resistances ofthe t two :6.,Inar'signaling system, a group oisig' naling conductors similarly subjected to con1 ditions producing variations in their transmission eiiiciency, al pilot circuit subjected to the 'same conditions .as-the signaling condoctors,v an apparatus for determining the adjustment tov-be made in the signalingcir-- cuits to compensate for the change in transmissionl said apparatus bei-ng bridged across the conductors of the pilot circuit a point intermediate the ends of 'said circuit so that ,the ioop'oii one side. ot 'the point `of connection lilas a greater resistance tlian that ofthe ioop on tue other side. and a fixed resistance in tbe loop ,havingn the small-.er resistance to compensate tor' ther my ,difference between ytlie resistances ot the twe Tos. f

signaling system, a group oi sip;v

naling conductors similarly" subjected to con". ditions producing variations in tbeir tranemission etloiencyg a pilotcicuit subjected ne saine conditions as tue signaling' and are i said pilot circuit at ai point intermediaiie the ends thereof; saidbridge being b ali'ancedL with' respect tothe vtwo sides 'ofthe fpilo't'v 8.- ln signaling system',- al of sig-:70 naling conductors similarly subjected t'ocon' ditioits producing i'iarialions in their. transiniss'ion eiiiciency, a pilot circuit subjected Y tothe saine conditions as the signaling conf "ductors, and adllheatstone bridge circuit in- 75.9

' ductors, and a'llVlieatstone bridge'ciic'uit .inf 90` cludinpfr a current responsive device, 'tlie terminals ot`- one of4 tbe arms` of the bridge` being connected across the conductors fof. said pilot circuit'at a point intermediateftbe ends" thereon so thatfvtlieloop of the Ypilot 95 circuit on oneside ofthe point of conne'ctionislonger `tlifa'n'the loop, on `the other side, and means included in the'sl'iorter loopv i to v'compensate fori-tbe diilference 4in 'the' length of the two loops. 110,0

l0. In a signaling system,A agroup o isig-4 naling conductors similarly subjected to condifions producing variations inV their ,trans-jy mission ctlicienojy,A a pilot ciicuit'subjected tothe same conditions as the 4signalingr con-1195 ductors, and a lVhcatstone bridge circuit in,- i cludinga current responsive device, the ter# ing conn'ectedacioss the conductors `o said pilot circuit ata point intermediate the ends ,U0

thereof., so that the'l'oop' of the pilot circuit on one sideof the point of connection'is longer than the 'loop on tlie .other side, andv a fixed resistance.v included intbe shorter oi2 the two loopsifto compensatef'tor tli'e 115 difference inthe length of the two loops.

"il, lin a signaling system a Pgroup ot'sigf :maling conductors similarly subjected to conditions producingy variations in their trans# mission eibciencjy` alpilotcircuit sul'ijected to 12"' ltiie same conditions as tbe signalingconduc-y tors, and a lililieatstone bridge'circuit includ! ing a current responsive device, the terminals of oneotlie' arms oftlie bridge be-,.,

ing connected' across the vconductors ot said 125 l l i .fpiiot circuit at a point intermediate the ends thereof; so 'that 'tii'e-,ioop ony one side ot the point of connect-ion li'as a pgrcatei,"resistance than .the 'loop on the otiierside, and

snmller resistance to compensate for the li'tl'ercoou hot/worn tho rsstance olf the two loops.

l2. In L signaling system, sgroup of signaling conductors simlarly subjected to con- (ltons producing vzxrattons in their trdlnu mission efcenry, u pilot Circuit subjected to tho same conditions as the signaling conductors, and n lllheutstone hrhlgo rrcut ncluding .a current responsive device, the ton nriuztls of one of the arms of the bridge being Connex-ted across the conductors of said pilot circuit ut n point nterrnedate the ends thereof, so that the loop on one side of the point ol connoction has :L greater resistance than the loop on the other side, und a lxed resistance in the loop` having the smaller resistance to compensate for tho difference bet-Woon lthe resistancos of tho two loops.

In testimony whereof 1 have, signed my namo to this spoccaton this 8rd (lay ot lVIarCh', 1921.

Grammi@ onrssoN. 

